To form source and drain regions on active areas defined on a substrate of semiconductor material on which the gate electrodes have been formed, a recent technique (large-angle tilted-implant diffusion: LATID) provides for doping ions to be implanted at angles which deviate considerably, for example by 45.degree., from a direction perpendicular to the surface of the substrate. In comparison with normal perpendicular implantation, this technique favors penetration of the dopant under the gate electrode and hence reduction of the distance between source and drain, that is, of the channel length, and improves the coupling between the gate electrode and the source and drain junctions. This technique is particularly advantageous when very small transistors (with channel lengths less than 1 .mu.m) are to be produced.
Continuously rotating implanting devices in which the doses of dopant to be implanted and the geometrical parameters (inclination of the beam of ions to be implanted, orientation of the beam to a reference line, speed of rotation) are regulated and supervised automatically have been constructed for performing tilted implants of this type. However, this equipment is very expensive.
Conventional fixed implanting devices may be used to obtain essentially the same results, the implantation being performed in several successive steps with a constant angle of inclination, but different orientations of the ion beam so as to achieve substantially uniform penetration of the dopant under the gate electrodes for any orientation of the strip which is to define the gate electrode. Typically, eight or sixteen implantation steps are performed with beam directions, or rather perpendicular projections of the beam onto the front surface of the substrate, arranged 45.degree. or 22.5.degree. apart, respectively. However, this method requires a fairly long processing time and, naturally, a corresponding long period of using the implanting device.